TRAP sequence (Twin-reversed arterial perfusion sequence) is a very rare complication of monochorionic twin pregnancies. Prevalence is 0.3:10,000 pregnancies. It results from a vascular communication between the acardiac twin and the pump (donor) twin. Acardiac twin is a parasitic twin with incomplete develoment of head, arms and heart. The pump twin does not usually show any abnormalities, aside from those associated with heart failure. Due to artery-to-artery and vein-to-vein anastomosis the acardiac twin receives blood supply retrogradely from the pump twin. This retrograde perfusion interferes with normal cardiac development of the acardiac twin. The arterial blood flow is reversed, that means arterial blood flows from the placenta towards the acardiac twin via the acardiac umbilical vein.

Complication can result in the congestive heart failure of the pump twin especially in case if the large weight of the acardiac twin (94% in case the weight of the acardiac is more than half of the pump twin weight).

Management includes either interruption of the circulatory anastomosis among pump and acardiac twin or at least controlling a possible heart failure of the pump twin. Blood supply to the acardiac twin can be disrupted via laser therapy; laser coagulation (bipolar forceps); umbilical artery embolization; endoscopy clamping. Cardiac output of the pump twin with the incipient heart failure can be managed by digoxin administration to the mother. In case of severe polyhydramnios, amniodrainage or indomethacin administration is a symptomatic treatment option.

Case report

We report a case of a spontaneous monochorionic diamniotic twin pregnancy which resulted in TRAP syndrome. A 31-year-old G1P0 was referred to our department at 10 weeks of pregnancy. Hydrops and possible arthrogryphosis of one of the fetuses were diagnosed. A scan at 12+6 wks showed hydrops of the affected fetus with lower then normal growth of the upper and lower extremities. The second twin was normal (Images 1,2).The patient decided for the conservative management.

The affected twin lacked cardiac acitvity by the 15 week. The second twin had a transient zero flow in the ductus venosus which quickly improved into normal range. Ultrasound scan at 20 weeks showed no abnormalities.

Scan at 22 weeks showed slight increase in the size of the polycystic mass of the acardiac twin (measuring 14x8 cm). Doppler did not show any twin-to-twin placental anastomosis. Second twin showed linear growth, normohydramnios and normal Doppler measurement (Image 3,4). Gestational diabetes was diagnosed at this time and patient was put on a diet.

A scan at 28 weeks detected a further increase in the size of acardiac fetus mass (measuring 22 cm in diameter). Placental anastomosis could not be detected. The pump twin showed no abnormalities (Image 5).

The patient was hospitalized at 31 weeks for an extensive thrombosis of the vena femoralis, LMWH (low molecular weight heparin) therapy was initiated, gestation diabetes well controlled by diet. The pump twin had normal MCA and umbilical artery Doppler, EFW=1300g corresponding with 28+5wks, normal amoput of fluid, no signs of heart failure. Blood flow in the abdominal aorta of the acardiac fetus was detected (Video 1); the cystic mass measured 30 cm in diameter (Images 6,7).

Delivery via Cesarean section was perfomed at 31+3 weeks due to worsening of the mother condition – thrombosis, progressing dyspnea, large edemas. The donor (pump) twin delivery weight was 1200 g and it measured 40 cm, Apgar score 8/9/9 (1st/5th/10th minute respectively) had no breathing difficulties and is doing fine. The acardiac twin’s weight was 2850g and it measured 30 cm (Image 9). There was a visible anastomosis on the placenta (Image 10). The patient fully recovered after delivery.

Conclusion

The case report has fortunately a favorable outcome. We decided for a conservative management following the patient’s wish. The cord occlusion or any other invasive technique was too risky later on. We followed the patient carefully especially the heart performance of the pump fetus which luckily did not show any signs of the heart failure although the risk was very high considering the weight of the acardiac twin.

Images 3,4: Images show an acardiac twin, visible spine, head and multicystic mass behind the spine.

Images 5,6: Image 5 show an acardiac twin at 28 wks, growth in size of the fetal mass is visible; Image 6 shows the acardiac twin at 31 wks.

Image 7, Video 1: Image 7shows a voluminous multicystic mass of the acardiac twin; Video 1 shows a flow in the umbilical aorta of the acardiac twin. The cephalic pole of the acardiac is on the top right of the video, and note the RED pulsating flow in the aorta.